Sockets are well known in the art. The two most common types are english (or S.A.E.) and metric sockets designed for driving hexagonal nuts. As the nuts come in a variety of sizes, there is one socket for each size of nut.
For example, a 1/2 inch socket is provided for a 1/2 inch diameter nut, a 9/16 inch socket is provided for a 9/16 inch diameter nut, and 5/8 inch socket is provided for a 5/8 inch diameter nut. Similarly, a 10 mm socket is provided for a nut having a 10 mm diameter. The sockets are typically sold in sets. One popular inexpensive set has S.A.E. and metric sizes, the S.A.E. sizes running from 3/16 inch to 3/4 inch, and the metric sizes running from 4 mm to 19 mm. In all, there are 16 S.A.E. sockets and 18 metric sockets. The tool box or socket caddy is provided with a series of recesses, there being one recess or retainer for each socket. The sockets in this set have indicia on one side only, which is typical, thus requiring that the socket be turned in a proper orientation so that its size may be read. Because of this, it is frequently difficult not only to select a socket for work, but also to properly put the socket back into its matching socket recess after a job has been completed. Also, it is difficult to tell metric from english sockets without reading the dimensions from the sockets. In many jobs today both english and metrics nuts are used requiring the worker to have two sets of sockets on hand during a job, or a combined set of the type referred to above. No matter how neat the worker may be, eventually the sockets become mixed, and it would facilitate his work if he could readily identify which sockets were metric, and which were english, and could also quickly identify the size without rotating the sockets.